The Williams Score Motor annotation is a little confusing and sometimes inconsistent. They did however publish at some point a decoder ring:
Williams score motor cam switches (resized).jpg
The helpful intention is that the switch label is supposed to give you some timing context which should make unwinding a circuit involving a score motor sequence a little easier. So for example a switch labeled 2A (on cam 2) will close momentarily before any switches labeled 3A (on cam 3) or with any higher number. When they did it consistently on a schematic it made things clearer than Gottlieb's notation for example (where 2B happens after everything else). Unfortunately I think these labels were sometimes inconsistent which made things a little worse.

Williams schematic symbols (resized).jpg

These diagrams are from Williams' Intro to Coin Operated Amusement Games available here and other places:
https://archive.org/details/introductiontocoinoperatedamusementgames

/Mark

I've seen similar issues with O and C score motor switch labels and don't have a good explanation for that, hence the inconsistencies I mentioned earlier.

I don't know. Sometimes the schematic will tell you something about the state of the machine, but often it won't, or it will only give you clues like this:
Williams schematic note (resized).jpg
If you're lucky, maybe there won't be any active relays when the game is reset but not unplugged so it won't matter.

Thanks for pointing that out. I had overlooked that. Now I wonder if Bally ever specified how their schematics were drawn.

I combed through all of the technical manuals I could find while preparing materials for my class and have posted snippets in the forum like the one above that folks seem to appreciate. If that makes me a nerd I'm good with that. While going through that exercise I discovered that big chunks of the manuals from two of the manufacturers are word for word the same which makes me wonder who actually wrote them.

I recently ran across this nugget on the Williams Skill Pool schematic on ipdb.org:
Skill Pool Motor switch nomenclature (resized).jpg
I think the position of the movable part of the switch (above or below the 2nd contact) also is meant to show NO vs NC switches.

This game (Skill Pool) uses a 2 cam score motor with a vertical shaft that looks more like a Gottlieb score motor. There's a complete diagram of it on the schematic. The position referred to above indicates which switch stack the switch is in. I suspect though that the number also indicates the relative timing of the switches just like it would on a horizontal shaft score motor with multiple cams.

These are normal 2 leaf score motor switches. The first is Normally Closed and the second is Normally Open. Note that these symbols are rotated clockwise 90 degrees when they're used in the schematic.

The schematic has lots of other interesting symbols that take a little detective work to sort out. Here are some examples:
Skill Pool Motor schematic symbols (resized).jpg